1. Field of the Invention
The present invention relates to a projector such as a liquid crystal projector, and the focusing method thereof.
2. Description of Related Art
In a liquid crystal projector, in general, a light beam emitted from a light source is made incident upon a liquid crystal panel (referred to as an LC panel), so that the light transmitted through the LC panel is projected onto a screen through a projection lens system which consists of a condenser lens and an image forming lens. In a conventional LC projector, the condenser lens is secured to the LC panel and gathers the light transmitted through the LC panel. Consequently, it is necessary to move the imaging lens (image forming lens) in the optical axis direction in order to vary the projection magnification (projection distance).
In the type of LC projector mentioned above, the projection magnification range is small, and accordingly, focusing can be effected by the movement of the imaging lens. The assignees of the present application are developing an optical system for an LC projector in which a super wide angle projection lens system is used to reduce the projection distance and thereby make the LC projector smaller, while at the same time making it possible to vary the magnification between a few times and several tens of times. Through the attempt to provide a new LC projector, it has been found that if only the imaging lens is moved in the optical axis direction, in accordance with the change in the magnification, no collimated light perpendicularly incident upon the LC panel can reach an entrance pupil of the imaging lens. Consequently, neither a high quality image can be projected, nor desired characteristics of quantity of light can be obtained. In other words, only light incident upon the LC panel at an incident angle which is not zero, i.e., light other than that normal to the LC panel, can be made incident upon the entrance pupil of the projection lens system. The contrast of the LC panel has a reliance upon the angle of light incident thereon. Namely, the contrast decreases as the deviation of the incident angle from the normal incidence increases (incident angle=0) and no high quality image can be obtained.